Quaternions can be added, subtracted, multiplied and divided like ordinary numbers, but there is a catch.

So we may use the ordinary numbers.

I don't mind bats in ordinary numbers.

Against ordinary numbers we are pretty strong, but against the hosts our enemies seem able to bring everywhere there is no calculating.

Nine, multiplied by each of the ordinary numbers, produces an arithmetical progression, each member whereof, composed of two figures, presents a remarkable fact; for example: